# mongodump -uuser -ppass --host 127.0.0.1 -o /backups/test1
connected to: 127.0.0.1
Thu Oct  4 20:06:42 all dbs
Thu Oct  4 20:06:42 DATABASE: admin      to /backups/test1/admin
Thu Oct  4 20:06:42     admin.system.users to /backups/test1/admin/system.users.bson
Thu Oct  4 20:06:42 doing snapshot query
Thu Oct  4 20:06:42              2 objects
Thu Oct  4 20:06:42     Metadata for admin.system.users to /backups/test1/admin/system.users.metadata.json
Thu Oct  4 20:06:42 DATABASE: test       to /backups/test1/test
# ls /backups/test1/
admin  test
# mongorestore -uuser -ppass /backups/test1/

connected to: 127.0.0.1
assertion: 13106 nextSafe(): { $err: "Invalid ns [.$cmd]", code: 16256 }